Genetically-encoded X-ray-sensitive tags for site-specific imaging of protein in cells. a, Schematic showing of APEX2 as genetically encoded tags for protein localization with XRM. Through using fusion expression plasmids including APEX2 and biotargets, they have high specificity. Following catalyzing the polymerization of DAB into localized X-ray visible dense DAB polymers, they localize and image various cellular targets with high resolution. b, XRM images of cellular proteins and specific amino acid sequence: COX4 (mitochondrial), Cx43, α-tubulin, β-actin, NLS and GalT. Scale bars: 10 μm.